如果您分享一个RefCell
那么它总是有可能发生变异——这本质上就是它的全部意义。鉴于您能够更改的实施LibraryStruct
,你可以确保data
不是公开的,并通过 getter 方法控制它如何暴露给用户:
pub struct LibraryStruct {
// note: not pub
data: Rc<RefCell<LibraryData>>
}
impl LibraryStruct {
// could also have returned `Ref<'a, LibraryData> but this hides your
// implementation better
pub fn data<'a>(&'a self) -> impl Deref<Target = LibraryData> + 'a {
self.data.borrow()
}
}
在您的其他结构中,您可以通过将其视为参考来使事情变得简单:
pub struct A<'a> {
data: &'a LibraryData,
}
impl<'a> A<'a> {
pub fn do_something(&self) {
// self.data is only available immutably here because it's just a reference
}
}
fn main() {
let ld = LibraryData {};
let ls = LibraryStruct { data: Rc::new(RefCell::new(ld)) };
let a = A { data: &ls.data() };
}
如果您需要将参考保留更长时间,在此期间原始RefCell
需要在库代码中可变地借用,那么您需要创建一个可以管理它的自定义包装器。可能有一个标准库类型,但我不知道它,并且很容易专门为您的用例制作一些东西:
// Wrapper to manage a RC<RefCell> and make it immutably borrowable
pub struct ReadOnly<T> {
// not public
inner: Rc<RefCell<T>>,
}
impl<T> ReadOnly<T> {
pub fn borrow<'a>(&'a self) -> impl Deref<Target = T> + 'a {
self.inner.borrow()
}
}
现在在您的库代码中返回此内容:
impl LibraryStruct {
pub fn data<'a>(&'a self) -> ReadOnly<LibraryData> {
ReadOnly { inner: self.data.clone() }
}
}
当你使用它的时候,内在RefCell
将无法直接访问,并且数据只能不可更改地借用:
pub struct A {
data: ReadOnly<LibraryData>,
}
impl A {
pub fn do_something(&self) {
// data is immutable here
let data = self.data.borrow();
}
}
fn main() {
let ld = LibraryData {};
let ls = LibraryStruct { data: Rc::new(RefCell::new(ld)) };
let a = A { data: ls.data() };
}